Abstract: A flexible heating wire includes a first conductive body, and a second conductive body, a thermally fusible electrically insulative body arranged such that the first and second conductive bodies will be brought into electric contact with each other when the thermally fusible electrically insulative body is thermally fused. Further provided is a third conductive body and a heating body having a positive temperature coefficient and held in electric contact with at least one of the first and second conductive bodies and the third conductive body. The flexible heating wire is capable of self-controlling the temperature of the heated heating body. The flexible heating wire can detect the danger of localized overheating, abnormal overheating, or the generation of an arc which is caused when the heating wire is subjected to external oppression, bending, or twisting, or when the heating wire is heated by an external source, or when a conductive material has been mixed in the PTC heating body.

Abstract: This invention provides a PTC heating wire (12), (13) of a tubular or band form which comprises a pair of electrodes (2), (2'), a PTC resistor (3) provided between the electrodes, and an insulative sheath (4) covering the electrodes and resistor, in which a numerical formula for setting a resistance, R.sub.E, within a tolerance range including an optimum resistance value is first determined. In practice, the resistance, R.sub.E, of the electrodes (2), (2') is properly determined, according to use conditions, using the numerical formula, thereby obtaining a PTC heating wire which ensures safe service.

Abstract: A cabinet for a loudspeaker is disclosed, which has a duct communicating the inside and outside of the cabinet. The duct includes a first duct section open to the inside of the cabinet and having a substantially constant sectional area and a second duct section extending from the first duct section toward the outside of the cabinet, the sectional area of the second duct section being gradually increased from the first duct section toward the outside of the cabinet.

Abstract: A flexible heating wire includes a first conductive body, a second conductive body, a thermally fusible electrically insulative body which are arranged such that the first and second conductive bodies will be brought into electric contact with each other when the thermally fusible electrically insulative body is thermally fused, a third conductive body, and a heating body having a positive temperature coefficient and held in electric contact with at least one of the first and second conductive bodies and the third conductive body. The flexible heating wire is capable of self-controlling the temperature of the heated heating body. The flexible heating wire can detect the danger of localized overheating, abnormal overheating, or the generation of an arc which is caused when the heating wire is subjected to external oppression, bending, or twisting, or when the heating wire is heated by an external source, or when a conductive material has been mixed in the PTC heating body.

Abstract: An aromatic polyimide composition usable for producing shaped articles, for example, films, or as varnish, lacquer, or bonding agent, comprises a high molecular weight aromatic polyimide resin which is a polycondensation-imidization product of an aromatic tetracarboxylic acid component comprising 50 molar % or more of 3,4,3',4'-biphenyltetracarboxylic acid, anhydride, salt, or ester with an aromatic diamine component including 50 molar % or more of 4,4'-diaminodiphenylether, and which is dissolved in a mixed solvent consisting essentially of 10% by weight or more of a first solvent component selected from naphthol and resorcin and the balance of a second solvent component selected from phenol and cresols.

Abstract: An aromatic polyamic acid solution composition useful as an electrically insulating varnish, comprises (1) an aromatic polyamic acid which is a polymerization product of (A) a tetracarboxylic acid component containing at least 80 molar % of the sum of (a) a first acid ingredient consisting of 3,3',4,4'-biphenyltetracarboxylic dianhydride and (b) a second acid ingredient consisting of at least one member selected from the group consisting of pyromellitic dianhydride, and 3,3'4,4'-benzophenone tetracarboxylic dianhydride, the molar ratio of the first acid ingredient to the second acid ingredient being in the range of from 30:70 to 75:25, with (B) an amine component consisting of at least one aromatic amine in a molar ratio of the tetracarboxylic acid component to the amine component of from 97:100 to 103:100, and which polymeric acid has a logarithmic viscosity number of from 0.1 to 1.5 determined in a concentration of 0.5 g/100 ml in N-methyl-2-pyrrolidone at a temperature of 30.degree. C.

Abstract: An aromatic imide polymer laminate material usable as a flexible circuit board substrate is produced by the process comprising coating a surface of a metallic foil with a solution of an aromatic imide polymer comprising at least 90 molar % of recurring unit of the formula (I): ##STR1## wherein R is a symmetrical bivalent aromatic radical having no substituent, and dissolved in a solvent consisting essentially of at least one phenolic compound; and heat drying the resultant solution layer to form an aromatic imide polymer solid layer firmly bonded directly to the metallic foil.

Abstract: An aromatic polyimide resin composition useful for producing a film or sheet, comprises 2% by weight or more of an imide polymer having at least 90 molar % of a recurring unit of the formula (I): ##STR1## wherein R' is a divalent aromatic radical, and dissolved in an organic polar solvent consisting essentially of one or more halogenated phenol compounds of the formulae (II) or (III): ##STR2## wherein R.sup.2 is a hydrogen atom of a C.sub.1-3 alkyl radical and is a halogen atom, the halogenated phenol compound having a melting point of 100.degree. C. or less and a boiling point of 300.degree. C. or less.

Abstract: Insulated electric power cables comprising a cured insulating material applied over a conductor and a layer of plastic compound comprising 100 parts by weight of a thermoplastic resin and 5-70 parts by weight of calcium oxide as a moisture-absorbing agent, overlying the insulating material and, optionally, lying between the conductor and the insulating material. The presence of calcium oxide serves to absorb steam before it penetrates into the insulating material through the layer of plastic compound being cured by steam, whereby the cured insulating material is free of microvoids and possess good insulation characteristics.